Prior art aluminum step ladders are generally made of aluminum and comprise two front aluminum leg tubes, two back aluminium leg tubes, one or more bottom aluminum step and a top step made of a material. The two front leg tubes and the two corresponding back leg tubes joint pivotally, so that the front leg tubes and the back leg tubes can open up to form a herringbone supporting structure. The one or more bottom step is connected between the two front leg tubes. The number of the bottom steps depends on the height of the ladder. The higher the ladder is, the more bottom steps the ladder has. For a step ladder, it generally has one or two bottom steps, but may have more. The top step is connected between the two front leg tubes and the two back leg tubes. The front portion of the top step joints pivotally with the two front leg tubes, and the rear portion of the top step joints pivotally with the back leg tubes through a connecting member. When the front leg tubes and the back leg tubes are in an open position, the top step positions the front leg tubes and the back leg tubes, so the ladder opens up. When the front leg tubes and the back leg tubes are in a folded position, the top step is stored in the space between the front leg tubes and the back leg tubes. The top step provides a standing surface for the user, so the top step is generally bigger than the bottom step. If the top step is entirely made of full aluminum material, the manufacturing may be difficult, and may need more materials, thereby increasing the cost and reducing the competitive advantages of the products.